What he means by "trickle down isn't a thing" is that there is no theory or school of thought called "trickle down economics". If your knowledge of economics comes from reading left wing critiques of economics and not actual economics (whether by left tor right wing economists) you can be forgiven for thinking there is something called "trickle down economics". It was a term coined by a editorial writer in the 80s to critisize reagan. He wasn't critisizing any actual well defined economic ideas, he was critisizing a political platform influenced by the Chicago school, but it was an innaccurate caricature of some Chicago school economics. There is no economist saying "hey if you give money to the rich it will trickle down to the poor". There are economists saying things like "if you make business hard to do then you will make people poorer in general " but in economics this usually comes with subtle discussions about trade-offs (sometimes we can accept lower production and fewer jobs [in some sense poorer] if it means we can have cleaner environment with environmental regulaions. Not always a bad thing. )

When I was 19 everything I knew about economics came from reading Noam Chomsky and Howard Zinn and various sociologists and critiques of "neoliberalism" (which is something like "trickle down economics" in that it doesn't actually describe a real economic school of thought), but at some point I actually read economics and you can imagine how shocked I was to find it wasn't just a bunch of right wing idiots who had never given any thought to the well-being of the unwashed masses. It's a discipline full of subtle thinkers from all political spectrums (not just Libertarians mind you, there aren't actually that many libertarians in academic economics), and you might get something out of it if you actually bother to read economics from economists not just critiques of economics from non-economists. There are a lot of disagreements in the discipline (as any healthy social science) but there is a lot of consensus too. (you can always find one or two quacks saying something crazy in any discipline---think about the 3% of climate scientists who don't believe in global warning).